Molecular replacement using DNA helical symmetry

The efficiency of molecular-replacement methods in the structure analysis of B-DNA is markedly increased if a knowledge of the structural properties and helical symmetry of B-DNA is incorporated into molecular-replacement procedures. The separation of the most significant or most robust parameters, such as the location of helices in the unit cell, from the less well defined parameters, such as rotation around the helix axis, further improves the reliability of molecular replacement and avoids frameshift errors in the positioning of the model. This approach has been applied successfully to solve novel structures of four B-DNA decamers in various space groups.